1. Field of the Invention
The present invention relates generally to an apparatus and method for adjusting a white balance. More particularly, the present invention relates to an apparatus and method for adjusting a white balance of an image captured with a complex light source.
2. Description of the Related Art
Cameras express most proper colors under an arbitrary light source via an Auto White Balance (AWB) function. Light input to a sensor of a camera depends on a spectrum of a light source and a reflection spectrum of a subject. When a White or Gray subject is exposed by a low or high color temperature light source, the White or Gray subject is expressed Red by the low color temperature light source and Blue by the high color temperature light source. The AWB function compensates for this (i.e., expresses a White color as is).
An AWB function allows a Gray area to be extracted under a complex light source and allows a Red gain (Rgain: G/R) and a Blue gain (Bgain: G/B) to be obtained so that percentages of Red (R), Green (G), and Blue (B) are the same in the Gray area. The Rgain and the Bgain are multiplied by each pixel in a whole image as a white balance gain, which is calculated and applied according to the Gray area regardless of the presence/absence of a human face in the image.
Estimating a Gray area is the core of AWB technology, and various technologies show relatively high performances under a single light source. However, since various Gray areas having different reflection spectral characteristics may be present under a complex light source, it is difficult to extract a proper Gray area, resulting in decreased AWB performance.
In particular, in an image including a human face that is captured under a condition where the face is exposed by a high color temperature light source while a background is exposed by a relatively low color temperature light source, if a white balance is adjusted to be suitable for the background, a facial color may be expressed bluer than an actual facial color, resulting in the face appearing lifeless.